The only rule is “it has to sound good”.
When I do trance, I try to figure out which tunes musically meld and thus try to keep “dead points” from happening. I mentioned to you before that if you feel the tunes you’re playing aren’t arranged the way you prefer, then go into a sound editing program and make your own edits. It’s a long tradition in DJing, and you’ll see many of your favorite trance DJs doing this like crazy.
I’m sure when we see more trance releases as STEMS, this will become much easier to do live.
In my book, trance blends should be smooth, and especially try to time them so one tune “lets off” while the new incoming tune “kicks up”. Beyond that, don’t pressure yourself too much. The crowds aren’t as picky on all this as we DJs are. I’ve been into ReOrder a lot lately, but even I’ll notice his blends are simplistic and fast. Not how I’d do things, but then again, I’m not ReOrder and he’s not me.